Submarines were a vital asset to both the Allies and the Axis forces during the Second World War. Hitler’s U-boat strategy to starve Europe (and especially the United Kingdom) through sinking merchant shipping from the United States only failed by the narrowest of margins.
On the Allied side, United States submarines would prove pivotal in the fight for the Pacific, achieving the impossible. The USS Archerfish, a US sub, even succeeded in sinking a Japanese aircraft carrier.
And then there was the Surcouf, the strange French interwar entry into the world of underwater conflict. Clearly the French had taken note of all the lessons learned from submarine development over the previous decades, and then decided to do something completely different.
In honesty, the French “cruiser submarine” Surcouf was already a decade old at the start of World War 2. When it was launched in 1929, she was without parallel in the world and remained the largest and most heavily armed submarine until World War Two.
The concept of a cruiser submarine was influenced by the German Navy’s unrestricted U-boat warfare during World War One. French planners envisioned a submarine that operated in the same way, moving silently and independently for extended periods of time without the need to return to port, attacking enemy merchant ships.
Initially known as “Project Q”, this plan required a much larger submarine than normal, with provisions for up to 90 days at sea. The armament would have to be economical and practical, so she was designed to mount large naval guns with fewer torpedoes than normal.
Surcouf was truly huge for the time. Although only 15m (49 feet) longer than the US Gato class submarine, she had almost twice the internal volume. However this resulted in a less efficient design and she operated with almost three times the crew complement compared to other submarines.
Surcouf had a twin-gun turret with 203 mm (8-inch) guns, the same caliber as the guns of a heavy cruiser, provisioned with 600 rounds. She was designed to function like an “underwater heavy cruiser” and was intended to seek out and engage in surface combat.
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The boat was still dangerous below the waves, equipped with as many as ten torpedo tubes: four 550 mm (22 in) tubes in the bow and two smaller groups of three towards the aft, designed to pivot so the entire boat did not have to align with the target.
She was designed to surface quickly and take the target unawares, destroying her in short order with her deck guns. These could fire up to 11km (6.8 miles) unaided, 16km (10 miles) using the periscope in calm seas, and a staggering 26km (16 miles) using an observation plane to assist, all within three minutes of surfacing.
Why Only One?
The French envisioned Surcouf to be the lead boat in a class of cruiser submarines operating independently across the globe. However, despite the apparent effectiveness of the design, only one was ever built.
However, soon after her launch in 1929 the London Naval Treaty was agreed between Japan, Italy, the United States, the United Kingdom, and France. Designed to curtail a naval arms race and limit naval power, among other things this treaty prevented the nations from operating more than three large submarines.
An exception in the treaty was included for Surcouf at the insistence of the French. However the dream of a fleet of these submarines was now impossible. Surcouf would be the only one of her kind.
Surcouf’s wartime activities were almost over before they began. In 1940, Surcouf was being refitted in Brest and was barely seaworthy when the Germans invaded France. In a desperate race to escape German capture she headed to sea with only a single engine and extremely limited rudder control, managing to make it to Plymouth in the United Kingdom, and safety.
The British, refusing to hand over Surcouf when the French surrendered, instead gave her to the Free French resistance. She would operate on the Allied side, largely in US and Canadian waters in the Atlantic, until a fateful night in 1942.
What Happened to Her?
On the 18th February 1942, about 130 km (80 miles) off the Panamanian coast, Surcouf was travelling towards the Panama Canal, and beyond that Tahiti. However, she never reached the canal entrance and after that night she was never seen or heard from again.
The American freighter Thompson Lykes, making passage from Guantanamo Bay in Cuba and in the same area, reported colliding with an unknown, partially submerged object which damaged the ship’s hull and keel. The night was especially dark and nobody from the freighter was able to identify what they had hit.
The American lookouts reported hearing people in the water, but the freighter carried on its course without stopping. When questioned about the incident they reported that they thought, despite hearing cries for help in English, that they had struck a German U-boat.
In the years since it has become increasingly likely that the Thompson Lykes had indeed hit and sunk the Surcouf, although this has never been conclusively proven. Her wreck has yet to be discovered, and there are alternative stories of her fate.
Other possibilities exist. The USS Mackerel and the USS Marlin, US submarines patrolling the Long Island Sound to the north, reported surprising a large submarine in the act of refueling a German U-boat. Both unknown submarines were sunk by the Americans.
This was obviously a much more explosive theory, as it would mean the Surcouf was secretly helping the Nazis. As a response to this theory, one million dollars was offered by a retired US Navy Captain to anyone who can prove that the Surcouf engaged in activities detrimental to the Allied cause. The prize is yet to be claimed, as of now.
There are many other, more unlikely theories. Some believe that the Surcouf was another victim of the Bermuda Triangle, or suggest that she was carrying a large cargo of gold bullion when she went missing. There are also stories that Jacques Cousteau, the renowned diver, explored the wreck in 1967, although these are unsubstantiated.
Diver Lee Prettyman had reported finding the Surcouf in the 1960s and there was a newspaper article about it with his picture in the Hartford Courant newspaper. However, the claim was retracted after Pretty man received threats, and he never disclosed where he thought the wreck to be.
James Rusbridger had examined some of the related theories in his book Who Sank Surcouf? He was able to dismiss all theories except one, which was related to the records of the 6th Heavy Bomber Group operating out of Panama.
The records show them sinking a large submarine on the morning of 19 February. Since, there is no data of a German submarine being lost in the area on that date, assumptions suggest that it could only have been Surcouf.
Wherever this strange submarine rests today, it can surely be only a matter of time before her wreck is found. Maybe in time there will be answers to her fate, too.
Top Image: Surcouf in the mid 1930s. Her unusually heavy armament can clearly be seen. Source: Unknown Author / Public Domain.
By Bipin Dimri
Wikipedia, 2022. French Submarine Surcouf. Available at: https://en.wikipedia.org/wiki/French_submarine_Surcouf
Sutton, H, 2018. Surcouf, The Ultimate Interwar Cruiser Submarine. Available at: http://www.hisutton.com/Surcouf.html
Military History Fandom, 2022. French submarine Surcouf. Available at: https://military-history.fandom.com/wiki/French_submarine_Surcouf